DOCSLIB.ORG

Can Spacetime Help Settle Any Issues in Modern Philosophy?∗

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Can Spacetime Help Settle Any Issues in Modern Philosophy?∗ Can Spacetime Help Settle Any Issues in Modern Philosophy?∗ Presented at the Issues in Modern Philosophy Conference at NYU November 10-11 2006 Nick Huggett Philosophy, UIC December 7, 2006 1 Introduction Deciding what to talk about in this paper was a challenge; perhaps contemporary phi- losophy offers no more possible topics to choose from than any of the individual figures considered over these two days, but what to present that might connect the historical pa- pers with contemporary philosophy? How to say something that might be informative and substantive and useful to an audience which likely comes from a historical background? One option was to discuss philosophical issues concerning contemporary spacetime physics – quantum gravity and string theory say. While that approach might show something of how philosophy continues to engage with emerging science, the danger is that attempts to relate such issues to historical concerns will be forced. I’ve opted instead to discuss a few influential ideas about how twentieth century math- ematics and philosophy can help understand and resolve early modern questions about the nature of space and time. In part I’ll be offering a map of the issues; I’ll be covering quite a lot of ground in a small time, but presumably it’s not entirely new to this audience. To be substantive as well as informative, I want to engage with the ideas I discuss. In particular, (i) I want to explore the limits of the mathematical theory of spacetime (more generally, differential geometry) as an analytical tool for interpreting early modern thought. While it dramatically clarifies some issues, it can also lead to misunderstandings of some of the figures that we have been considering here, and is a very poor tool indeed for others – Leibniz in particular. (ii) I will show how to blunt a very influential argument against a ‘relational’ conception of spacetime – the view that the properties and relations of bodies exhaust the spatiotemporal. ∗Thanks to Gordon Belot, Howard Stein and Daniel Sutherland for criticisms and comments on an earlier draft. 1 2 SPACETIME AND HISTORIOGRAPHY Draft: do not quote without permission There are two flaws in this paper that I wish to acknowledge from the outset. The first is that time constraints have forced me to bracket important contributions to the debate, notably, Friedman (1983); ultimately because that work is less concerned to use the spacetime formalism to do history of philosophy, and it doesn’t take me as directly to the substantive points I wish to make. The second flaw is that some of my criticisms of contemporary philosophers seem like nit-picking compared to the critiques that they made of their predecessors – in particular, my critique of the spacetime approach is within the tradition initiated by Stein et al, not a break from it. Still, I believe that an investigation of the limitations of that approach is timely and useful. 2 Spacetime and Historiography Howard Stein’s 1967 essay transformed the understanding of the so-called ‘absolute-relative’ debate within the philosophy of physics community (though probably not entirely in ways Stein desired). In particular, the use of the spacetime framework became, perhaps, the most important tool for those seeking to analyse the contributions of historical figures to the debate. In this section I want to describe some of the ways in which that tool has been used, attempting to distinguish the uses which are genuinely illuminating from those that are misleading. (Since I posted a draft of this paper, I have received some illuminating correspondence from Stein, for which I am very grateful. As a result I have made certain changes. Some are minor, while a couple are more significant regarding Stein’s intentions [but not my central concern with the limitations of the spacetime approach]. Some require further clarification, and in no case can I guarantee that I have not traded one misinterpretation for another.) 2.1 Newton Stein’s paper is multifaceted, but for our purposes, the crucial points are as follows: first, Newton’s postulation of absolute space and time can be understood in terms of a spacetime with the geometry of the Cartesian product of a three-dimensional and a one-dimensional Euclidean space, S × T . The crucial feature of the Cartesian product is that it induces projections of any event onto ‘simultaneous’ and ‘spatially coincident’ events: in particular, if a point of S × T is denoted p = (σ, τ), then the points (σ, t) for any t ∈ T are spatially coincident with p. According to Stein, Newton’s postulation of absolute time amounts to the postulation of T . But absolute space is the space of equivalence classes of coincident points, which itself has a natural three-dimensional Euclidean geometry. That is, absolute space is not simply S, but S in the spacetime S × T , in order to capture the idea of the persistence of spatial points through time.1 1Of course Newton implicitly takes absolute time to be ‘spread through’ space: simultaneity is absolute. In this sense absolute time is similarly not merely T , but the space of equivalence classes of simultaneous points, which itself has the same geometry as T . It is T in S × T . 2 2 SPACETIME AND HISTORIOGRAPHY Draft: do not quote without permission S × T – which we shall call ‘Newtonian’ spacetime (contrary to Stein’s usage) – makes absolute velocity well-defined; it is the velocity relative to the points of absolute space. And since absolute velocity is well-defined, so is absolute acceleration; indeed, Newton introduces the structure precisely because the latter quantity is required by his mechanics. But, as Newton’s Corollary V to the laws makes clear, the models of Newton’s laws are independent of absolute velocity; as far as the laws are concerned, the concept has no content. The ‘solution’ – not Newton’s, of course – is to apply a kinematical principle of ‘Galilean relativity’: view the natural spatial projection in S ×T as a representational arte- fact, and treat all projections at a constant angle to it – all ‘straight’ ones – as equivalent. This ‘Galilean’ spacetime lacks the structure to reidentify points over time – no one pro- jection is singled out as the correct one – and so does not support a well-defined quantity of absolute velocity. (Put another way, instead of a relation of spatial coincidence between pairs of non-simultaneous events, in Galilean spacetime there is a relation of colinearity between triples of points.) However, it is a simple but important fact that the accelera- tion of a body relative to the points identified by the natural projection is the same as its acceleration relative to the points identified by any straight projection; put another way, accelerations reckoned in one frame are equal to the accelerations in any other frame in constant, linear relative motion. Thus in Galilean spacetime there is a well-defined notion of absolute acceleration, but not of absolute velocity; it satisfies the kinematical presupposi- tions of Newtonian mechanics, without introducing unobservable motive quantities.2 Thus Galilean spacetime address a long-standing objection to Newton’s account of motion. Using the spacetime framework, Stein’s paper makes a number of important points. In particular, he explains how Newton’s ‘metaphysical’ speculations concerning absolute space and time can be logically separated from his ‘scientific’ discussions. On the one hand we have the ideas that space is ‘as it were’ God’s sensorium (Optiks, Query 28) or an ‘emanative effect of God’ (De Gravitatione). On the other, such remarks are absent from the Principia; moreover, absolute quantities of motion are in no way superfluous to mechanics. In the spacetime framework, with a 1/r2 force, it is indeed the case that the planets orbit the Sun (or rather the centre of mass of the solar system); in the sense given by the geometrical framework of either spacetime, the planets accelerate towards the Sun, not the Earth. Such quantities are crucial to Newton’s project, and can be inferred from empirical phenomena – the observed motions of the planets; so insofar as absolute space is postulated to make them well-defined, it is scientifically respectable. (Of course, absolute space is still unempirical insofar as it makes absolute velocity well-defined; but Newton’s ‘error’ is not wilful deviation from scientific methodology, but failure to see how else to define absolute acceleration.) 2Actually, in a sense it doesn’t. As Newton demonstrated in Corollary VI, a system is indistinguishable from any other that differs only in a common acceleration of its parts: for instance, a closed system in inertial motion is indistinguishable from an identical system in free-fall. Perhaps one should conclude that the ‘common acceleration of the whole’ is not a well-defined quantity either; but it is well-defined in Galilean spacetime and prima facie by Newton’s laws – the systems experience different forces. 3 2 SPACETIME AND HISTORIOGRAPHY Draft: do not quote without permission More generally, Stein wishes to show that Newton’s analysis in the Scholium (to the Definitions) vindicates his postulation there of absolute space and time. That is, the Scholium is not a gratuitous metaphysical intrusion in the Principia, but demonstrates the failure of ‘purely relative’ definitions of motion to agree with the concept of motion in mechanics, and uses those laws to investigate the empirical content of Newton’s concepts of motion. In Stein’s view, the vindication of absolute quantities requires only that Newton’s defi- nitions of ‘absolute’ concepts are clear and that they allow the formulation of true, substan- tial, empirical propositions.3 That is, they require a positive analysis of their ‘empirical content’.
Load more

Recommended publications
  • Arxiv:2103.15570V2 [Physics.Hist-Ph] 22 Jun 2021 to This Article in Its Purpose and Content
    An Analysis of the Concept of Inertial Frame Boris Čulina Department of Mathematics University of Applied Sciences Velika Gorica Zagrebačka cesta 5, 10410 Velika Gorica, Croatia e-mail: [email protected] Abstract. The concept of inertial frame of reference is analysed. It has been shown that this fundamental concept of physics is not clear enough. A definition of inertial frame of reference is proposed which expresses its key inherent property. The definition is operational and powerful. Many other properties of inertial frames follow from the definition or it makes them plausible. In particular, the definition shows why physical laws obey space and time symmetries and the principle of relativity, it resolves the problem of clock synchronization and the role of light in it, as well as the problem of the geometry of inertial frames. keywords: inertial frame of reference, space and time symmetries, the principle of relativity, clock synchronization, physical geometry The concept of inertial frame is a fundamental concept of physics. The opinion of the author is that not enough attention has been paid to such a significant concept, not only in textbooks, but also in the scientific literature. In the scientific literature, many particular issues related to the concept of inertial frame have been addressed, but, as far as the author is aware, a sys- tematic analysis of this concept has not been made. DiSalle’s article [DiS20] in the Stanford Encyclopedia of Philosophy gives an overview of the histori- cal development of the concept of an inertial frame as an essential part of the historical development of physics.
    [Show full text]
  • Principle of Relativity in Physics and in Epistemology Guang-Jiong
    Principle of Relativity in Physics and in Epistemology Guang-jiong Ni Department of Physics, Fudan University, Shanghai 200433,China Department of Physics , Portland State University, Portland,OR97207,USA (Email: [email protected]) Abstract: The conceptual evolution of principle of relativity in the theory of special relativity is discussed in detail . It is intimately related to a series of difficulties in quantum mechanics, relativistic quantum mechanics and quantum field theory as well as to new predictions about antigravity and tachyonic neutrinos etc. I. Introduction: Two Postulates of Einstein As is well known, the theory of special relativity(SR) was established by Einstein in 1905 on two postulates (see,e.g.,[1]): Postulate 1: All inertial frames are equivalent with respect to all the laws of physics. Postulate 2: The speed of light in empty space always has the same value c. The postulate 1 , usually called as the “principle of relativity” , was accepted by all physicists in 1905 without suspicion whereas the postulate 2 aroused a great surprise among many physicists at that time. The surprise was inevitable and even necessary since SR is a totally new theory out broken from the classical physics. Both postulates are relativistic in essence and intimately related. This is because a law of physics is expressed by certain equation. When we compare its form from one inertial frame to another, a coordinate transformation is needed to check if its form remains invariant. And this Lorentz transformation must be established by the postulate 2 before postulate 1 can have quantitative meaning. Hence, as a metaphor, to propose postulate 1 was just like “ to paint a dragon on the wall” and Einstein brought it to life “by putting in the pupils of its eyes”(before the dragon could fly out of the wall) via the postulate 2[2].
    [Show full text]
  • Reconstructing William Craig Explanation of Absolute Time Based on Islamic Philosophy
    Reconstructing William Craig Explanation of Absolute Time Based on Islamic Philosophy M. S. Kavyani (1), H. Parsania (2), and H. Razmi (3) Department of Philosophy of Physics, Baqir al Olum University, 37185-787, Qom, I. R. Iran. (2) Permanent Address: Department of Social Sciences, Tehran University, Tehran, I. R. Iran. (3) Permanent Address: Department of Physics, University of Qom, Qom, I. R. Iran. (1) [email protected] (2) [email protected] (3) [email protected] Abstract After the advent of the theory of special relativity, the existence of an absolute time in nature was rejected in physics society. In recent decades, William Craig has endeavored to offer an interpretation of empirical evidences corresponding to theory of relativity with the preservation of an absolute time. His strategy is based on two viewpoints including dynamical theory of time and the Eminent God’s temporal being. After considering and criticizing these two viewpoints, using the well-known overall substantial motion of nature in Islamic philosophy and thus the realization of a general time for all the nature, we have tried to reconstruct Craig argument for an absolute time. Although Craig has considered some evidences from modern physics reasoning on an absolute time, the special advantage of the approach considered here is in this fact that it connects better the existing gap between the metaphysics and the physics of the argument. Keywords: Absolute time; Theory of relativity; William Craig; The dynamical time theory; Islamic Philosophy; Nature overall substantial motion; General time Introduction In classical mechanics, the absolute universal time was considered as the measure of the events chronology and a parameter for determining their priority, posteriority, and simultaneity.
    [Show full text]
  • Relationalism About Mechanics Based on a Minimalist Ontology of Matter
    Relationalism about mechanics based on a minimalist ontology of matter Antonio Vassallo,∗ Dirk-André Deckert,† Michael Esfeld‡ Accepted for publication in European Journal for Philosophy of Science This paper elaborates on relationalism about space and time as motivated by a minimalist ontology of the physical world: there are only matter points that are individuated by the distance relations among them, with these re- lations changing. We assess two strategies to combine this ontology with physics, using classical mechanics as example: the Humean strategy adopts the standard, non-relationalist physical theories as they stand and interprets their formal apparatus as the means of bookkeeping of the change of the distance relations instead of committing us to additional elements of the on- tology. The alternative theory strategy seeks to combine the relationalist ontology with a relationalist physical theory that reproduces the predictions of the standard theory in the domain where these are empirically tested. We show that, as things stand, this strategy cannot be accomplished without compromising a minimalist relationalist ontology. Keywords: relationalism, parsimony, atomism, matter points, ontic structural realism, Humeanism, classical mechanics Contents 1 From atomism to relationalism about space and time 2 2 From ontology to physics: two strategies 11 ∗Université de Lausanne, Faculté des lettres, Section de philosophie, 1015 Lausanne, Switzerland. E- arXiv:1609.00277v1 [physics.hist-ph] 1 Sep 2016 mail: [email protected] †Ludwig-Maximilians-Universität
    [Show full text]
  • Newtonian Space-Time
    L1lCU .. l.HC I..i.~UU Ul 411 LU •••..)C .lU,)I.~1.lJ.LLol.L.LI".Uu..) ,)t'IA •••.••,•.) u.I...J.y v....I.UUU6.l..L1." V.L u.~ ...1...1••.• 10cIIs Of all pQHible eVeJlts; it is called "sp:l.ce-time." (3) The instant.l!!::ousthree-dimensional spaces, which so far as (2) goes are entirely separ.lte, form p:lrt of a luger connected, structure: sp:lce-time is, intrinsicallr, :z fOllr-dimensional real affine space-that is, it possesses a a notion of "str:light line," having the same properties in respect of inter- section (and. so also parallelism) as in a Euclidean space of four di- y REMARKS TODAY AND TO};!OR.~.OW WILL BE BASED UPON A RATHER mensions. (The stmight lines of space-time are to be thought of as repre- lengthy paper, written witl1severl1 simultaneous objectives: senting all F{)ssibleuniform rectilinear lIIotiollS.2) Moreover, the natural M. (I) To cast light upon the issues involved in a celebrated pass:lge of intel- projection of space-time upon T (assigning to every possible event its lectu:ll history, and incidentally to clarify some of the purely historical cir- "epoch" or "date") is an :lffine mapping; :lnd the Euclide:ln structures of cumstances; the insontar.eous spaces :lre compatible with their :lffine structures as the ( 2) By elucidating those is'sues, to help furnish insight on related questions of fibersof this ffi3.pping. current interest; The technicalities of this :l.ccountneed not too much concern those to whom they (3) To promote an attitude tow:lrd philosophical questions that was a prevalent :lreunfa.miliar; but it is important to remark that the structure required by (3), one in the seventeenth century, th3.tseems to me sound and admirable, and which I shall refer to as the "kinematical connection" of space-time, and which th:lt seems not to be prewaLenttoday.
    [Show full text]
  • Newton and Leibniz on Space and Time
    Newton and Leibniz on Space and Time Jeremy Safran and Jack Kissel Introduction • Can you explain the concept of motion without the notion of space and/or time? – Both Leibniz and Newton’s theories of space and time are rooted in observations of change (e.g. motion). • What is space and time? Are they real substances in the world? Can a single object or event have an absolute space or time, or do space and time rely on relational properties between multiple objects or events? A Few Definitions • Relativism - Leibniz’s theory on space and time • Absolutism – Newton’s theory on space and time • Plenum – a space every part of which is full of matter, which included air and ether • Void – space that contains no matter • Sensory organs – the tools with which we perceive the world. • Sensorium – the seat of sensation where an organism experiences and interprets the environment within which it lives Relativism • First, what are space and time? Are they real substances in the world or simply relational properties between objects and events? • “I hold space to be something merely relative… as an order of coexistences, as time is an order of successions” (Leibniz, L111.4, AW 297b). • For example: If the entire universe were moved 3 inches or 3 seconds from where it actually is, nothing in the universe would change in any significant (relative) way Absolutism • “Absolute space, in its own nature, without relation to anything external, always remains similar and immovable” (Newton, AW 285) • Humans can only observe relative space and time, but absolute space and time must presuppose the relative.
    [Show full text]
  • The Universe Be (Before Einstein)
    ACTIVITY ONE: NOVEMBER 7 THE UNIVERSE B.E. (BEFORE EINSTEIN) On November 7, 2014, Interstellar, a saga of courage, sacrifice, desperation and hope, will challenge moviegoers to think about the radical ways a changing Earth and the need to address its changes might challenge our daily ACTIVITY OVERVIEW: ACTIVITY GUIDELINES lives and the concepts that shape our existence. This film explores the often-startling aspects of the fabric of the universe, as understood by modern scientists. Interstellar will introduce you to scientific concepts that may These thought-provoking supplemental activities are designed to introduce the concept of relativity, and to give boggle your mind. In order to understand and appreciate those concepts, become familiar with the scientific ideas students a broader and deeper understanding of some of the fascinating science behind Interstellar. Use these activities introduced in these activities. as an introduction to the movie and its concepts, and then see the movie together (talk to your PTA!) or have students see the movie with their families and friends before embarking on post-movie discussions about the intriguing concepts and questions the movie raises. PART 1 It’s helpful to know how scientists understood motion through space for hundreds of years. Things like time ACTIVITY ONE: ACTIVITY TWO: ACTIVITY THREE: and distance were absolute: the same everywhere for THE UNIVERSE B.E. (BEFORE EINSTEIN) IT’S ALL RELATIVE CONCEPTUAL CLOCKS On November 7, 2014, Interstellar, a saga of courage, sacrifice, desperation and hope, will challenge moviegoers The universe we know and as depicted in Interstellar has a history of changed and challenging scientific understandings.
    [Show full text]
  • A Critical Analysis of the Concept of Time in Physics
    A critical analysis of the concept of time in physics Claudio Borghi Liceo Scientifico Belfiore, via Tione 2, Mantova, Italy Abstract. This paper puts forward a broad critical analysis of the con- cept of physical time. Clock effect is conceived as a consequence of the variation of the gravitational or pseudo gravitational potential, and it is remarked that only some real clocks measure durations in agreement with the predictions of general relativity. A probable disagreement is ex- pected between radioactive and atomic clocks, in the light of Rovelli’s thermal time hypothesis. According to the recent contributions by Rugh and Zinkernagel, the relationship between time and clocks is investigated in order to found on a physical basis the concept of cosmic time. In the conclusive section is argued the impossibility of reducing thermal time to relativistic time. Key words: Time, Relativity, Thermodynamics, Cosmology 1 Introduction The following points resume the main concepts: 1) analysis of the operational definition of time in Newton and Einstein; 2) distinction between time dilation effect and clock effect in Einstein’s theory; 3) considerations about the nonequivalence between atomic clocks and radioac- tive clocks in the light of the clock hypothesis; 4) remarks about the existence, in nature, of thermal clocks that do not behave as relativistic clocks, and about the consequent nonequivalence between ther- mal and relativistic time, in the light of the thermal time hypothesis; 5) reflections about the operational definition of cosmic time in relation to the physical processes, then to the clocks that can be used for measuring it; arXiv:1808.09980v2 [physics.gen-ph] 2 Sep 2018 6) conclusive remarks about the need of a revision and a consequent refounda- tion of the concept of time in physics.
    [Show full text]
  • Is Time Travel Possible?
    Lecture Notes 5: Is Time Travel Possible? 1 Special Relativity Thus far, we’ve been discussing some big questions concerning the whole Universe: Was there a beginning of time? Will there be an end? Is the Universe infinite? Are there parallel Universes? Does the Universe contain any intelligent life besides us? In these notes, I’d like to change the subject a bit and discuss the nature of space and time, particularly time and the question of whether time travel is possible. Time travel is certainly something we’ve all pondered before — perhaps wished for — but what do the laws of physics have to say about it? Is it possible to build some kind of a time machine to take us back to the 1960s, say, and see the Beatles? Or to travel to the far future and see what technology is like in the year 7,000? To get a hold on these questions, we need to understand what time really is. Our current understanding of what time is and what space is comes from Einstein’s theory of relativity. But, before I describe relativity, I’d first like to describe the way that people thought of space and time before Einstein — the way that Issac Newton envisioned space and time to be. I could simply begin with Einstein’s theory, but I think doing so would rob you of a full appreciation of its crazy brilliance. So we’ll talk about Newton briefly first. According to Newton, space and time were, in a sense, absolute. Space is the “stage” on which all the events of the Universe happen, and time is just this thing that passes at a constant rate for all objects in the Universe at all places.
    [Show full text]
  • Space, Time, and Ontology in Classical and Quantum Gravity
    WHATEVER IS NEVER AND NOWHERE IS NOT: SPACE, TIME, AND ONTOLOGY IN CLASSICAL AND QUANTUM GRAVITY by Gordon Belot B.Sc., University of Toronto, 1991 M.Sc., University of Toronto, 1993 Submitted to the Graduate Faculty of University of Pittsburgh in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Pittsburgh 1996 John Earman Joseph Camp Adolf Grünbaum John Norton Carlo Rovelli ii WHATEVER IS NEVER AND NOWHERE IS NOT: SPACE, TIME, AND ONTOLOGY IN CLASSICAL AND QUANTUM GRAVITY Gordon Belot, Ph.D. University of Pittsburgh, 1996 Substantivalists claim that spacetime enjoys an existence analogous to that of material bodies, while relationalists seek to reduce spacetime to sets of possible spatiotemporal relations. The resulting debate has been central to the philosophy of space and time since the Scientific Revolution. Recently, many philosophers of physics have turned away from the debate, claiming that it is no longer of any relevance to physics. At the same time, there has been renewed interest in the debate among physicists working on quantum gravity, who claim that the conceptual problems which they face are intimately related to interpretative questions concerning general relativity (GR). My goal is to show that the physicists are correct—there is a close relationship between the interpretative issues of classical and quantum gravity. In the first part of the dissertation I challenge the received view that substantivalism has a commanding advantage over relationalism on grounds internal to GR. I argue that this view is based on a misconception of the relationships between realism and substantivalism, and between empiricism and relationalism.
    [Show full text]
  • Kant, Gödel and Relativity1
    1 Kant, Gödel and Relativity1 Mauro Dorato Dept. of Philosophy Università di Roma Tre Via Ostiense 234 00146, Rome, Italy tel. +39-06-54577523; fax +39-06-54577540 e-mail: [email protected] Forthcoming in P. Gardenfors, K. Kijania-Placek and J. Wolenski (eds.), Proceedings of the invited papers for the 11th International Congress of the Logic Methodology and Philosophy of Science, Synthese Library, Kluwer, Dordrecht, 2002, pp.329-346. Abstract Since the onset of logical positivism, the general wisdom of the philosophy of science has it that the kantian philosophy of (space and) time has been superseded by the theory of relativity, in the same sense in which the latter has replaced Newton’s theory of absolute space and time. On the wake of Cassirer and Gödel, in this paper I raise doubts on this commonplace. I first suggest some conditions that are necessary to defend the ideality of time in the sense of Kant, and I then bring to bear some contemporary physical theories on such conditions. 1 What is “the problem of time”? Time is absolutely central in our inner experience, but at least since the foundation of modern physics, it also plays an important role in the description of the outer world. To the extent that there is a physical and a mental time, one can safely surmise that the problem of trying to establish whether and how they are related is one of the most fundamental issues in the philosophy of time. Are physical and mental time in conflict, or we can regard the former as some sort of appropriate extension to the outer world of the main features of the latter? These questions, important as they are, already presuppose, however, that there are two sides of the problem, namely that there is, at a fundamental level of description, a physical time.
    [Show full text]
  • Relativity of Simultaneity, in Order to Escape This Contradiction, Led Him to the Discovery of the Special Theory of Relativity
    Vot,. 16, 1930 PHYSICS: F. S. C. NORTHROP 55 4Proc. Nat. Acad. Sci., 7, p. 63, eq. (8). 5 Ibid., 7, p. 63, eq. 10. 6 Proc. Amer. Acad. A. S., 53 (1918), pp. 269-386. 7 I have not included cadmium in this list of metals. Bridgman studied cadmium as he did the eighteen other metals, but the value which he found for the Thomson effect in it is about ten times as great as that indicated by the observations of Fleming and Dewar (Phil. Mag., 40, 5th series, 1895). Bridgman expresses the opinion that the specimen of cadmium which he studied may have been in an unstable condition, between two allotropic forms. 8 Although I have arrived quite independently at the number 1.50 as the mean value of q in metals, I have already (Nat. Acad. Sci. Proc., 15, p. 507) called attention to the fact that Richardson in deriving his T2 emission formula from the "classical kinetic theory" assumed the number of free electrons per cm.' of a metal to be proportional to T1*5. 9 I have discussed evidence bearing upon this magnitude in a recent paper, "On Electrons That Are 'Pulled Out' from Metals," Proc. Nat. Acad. Sci., 15, 241-251 (1929). 10 J. Frank. Inst,~206, Oct., 1928. 11 Gauthier-Villars, Paris, 1927. TWO CONTRADICTIONS IN CURRENT PHYSICAL THEORY AND THEIR RESOLUTION BY F. S. C. NORTHROP DEPARTMENT OF PHLOsQWHY, YAIX UNIVERSITY Communicated November 29, 1929 When Einstein examined the electro-magnetic theory of Lorentz at the beginning of this century, he found the principle of relativity for Galilean frames of reference, and the principle of the absolute velocity of light in vacuo, to be experimentally valid, yet contradictory.
    [Show full text]